This invention relates to an image forming apparatus with a positioning-mark forming function and, more particularly, to an image forming apparatus for forming a color-separated original image required for forming an original plate in offset printing.
In recent years, graphic arts printing has developed markedly along with an advance in electronics, and electronic graphic arts printing has become very popular. In electronic graphic arts printing, the density of an image of an original is photoelectrically converted into an electrical signal and the electrical signal is subjected to predetermined processing to obtain a light intensity signal. The intensity signal is used to expose a film (photosensitive medium) with light. The exposed film is developed to prepare a negative or positive film for an original plate.
According to the above technique, however, the printing process is complicated and the printing equipment is bulky, thus resulting in high costs. A conventional system is designed to produce only graphic arts films and cannot be used for other applications.
In order to align graphic arts films (block copies) of the respective colors, positioning marks (so-called register marks) are manually adhered to graphic arts films, thus degrading operability and causing potential positional shifts.